Acrylic Thermal Contraction

[mDust]

Anyone that has a good memory or has accidentally clicked my sig may recall that I have been planning (for about a year now :down:) a full-submersion oil tank in which I will bathe my computer. Unfortunately, I keep thinking of features to add or upgrade so the design is ever-changing. Due to this terrible planning philosophy, I've been working on sub-zero temps to kick it up a notch. This has introduced numerous new considerations. A few of which are pretty serious: thermal expansion contraction of acrylic and other materials, large temperature variations, and insulation. I could design, some ridiculously expensive solutions to these problems, like expansion joints and vacuum chambers, but I'm not made of money and there are already enough points of failure in my tank. I can't just give up either...:)

I might just forget about sub-zero temps and just settle for below freezing temps instead.

My concerns are really centered around the thermal expansion/contraction of acrylic:

Comparison of Co-Efficient of Thermal Expansion

Acrylic Sheet vs. Other Materials
Inches/Inch/F
Acrylic Sheet .0000410
Aluminum .0000129
Plate Glass .0000050 http://www.rideoutplastics.com/faq.html#Expansion

Acrylic is out of control here. But I'm not an engineer and I'm not exactly sure how much stress this would cause over, say, an 80F span. I know that something has to give when a material cannot flex anymore. I just don't need cracks in an oil tank that is in my living room in a 3rd floor apartment; neither does my landlord or the guy that lives below me.

The expansion is measured in inches of expansion/contraction per linear inch per degree F... In theory, if I had a cube tank with all parts changing temperature simultaneously and all edges solvent welded, would the sides expand and contract in unison or would there be stress fractures all over the place?

I'm personally thinking that solvent welding would be a poor construction choice... Instead I could mechanically lock the edges with dovetails and seal them with silicone...although I've always thought that was an ugly option. It would work and provide a bit more 'give' to minimize stress.

Anyone have any other suggestions? Or comments? Or random, unrelated thoughts?

[x88x]

I haven't studied this, so don't take my word for it, but I would guess that the panels may expand/contract at the same rate, but the solvent is also going through the same temperature changes, so will also expand and contract. If you don't match the solvent expansion rate with that of the panel material, there will be problems...it might work if you can match them though.

If you're shooting for sub-zero temps, I think a bigger problem you're going to run into is insulation of the tank, to maintain those temps.

[mDust]

I haven't studied this, so don't take my word for it, but I would guess that the panels may expand/contract at the same rate, but the solvent is also going through the same temperature changes, so will also expand and contract. If you don't match the solvent expansion rate with that of the panel material, there will be problems...it might work if you can match them though.

If you're shooting for sub-zero temps, I think a bigger problem you're going to run into is insulation of the tank, to maintain those temps.

The solvent dissolves the acrylic and then evaporates leaving only solid acrylic behind. It's awesomely effective and a ridiculously strong bond...I couldn't break any of the test pieces I welded and I was trying as hard as I could...with leverage. Generally, the sheet itself would crack before the bonded seam did. I'm just worried that the same thing will happen when the pieces expand or contract.

I've been thinking on the insulation problem. I thought about a tank inside a tank with a near vacuum in between which gives about an R-10 insulation rating per inch. I'm not sure if 1) the acrylic and joints will structurally hold a vacuum, 2) I can maintain a vacuum, or 3) if that R-value is efficient enough (at just 1") to keep the compressor from running 24/7. This is why I was looking for argon or, preferably, krypton gas. Argon is actually a pretty lame insulator even though it is better than atmospheric air and krypton is about 60% better than argon. They would be my best bet assuming the vacuum fails.
I haven't looked at any equations yet, so.... /shrug
I could also run it normally well above freezing with the option of dropping it below for benching/OCing...especially since I'd rather not triple my electric bill. I put a lot of thought into this stuff, but it was all the wrong kind of thoughts. I was thinking bad ass thoughts instead of practical thoughts. :facepalm: